For example, there is a photodetecting device using the so-called photoconductive type sensor element which detects ultraviolet light irradiated to alight detecting unit by change of an amount of optically induced current of the light detecting unit.
As the photoconductive type sensor element, a silicon semiconductor etc. which have detection sensitivity in visible light etc. in a wavelength range from 400 to 750 nm are conventionally supposed.
A photodetecting principle of such as photoconductive type sensor element is to generate an electron-hole pair in a semiconductor by a photoelectric-conversion operation by irradiating with light which has an energy equal to or greater than the semiconductor bandgap of the light detecting unit, and to extract the above carrier to an external circuit by an externally-applied voltage to be detected as an amount of optically induced current.
The ZnO-based ultraviolet light sensor is also proposed.
It is known that metal oxide surface resistivity is subject to operational environment including oxygen concentration and humidity. Therefore a semiconductor type gas sensor usually makes use of the above phenomenon mentioned above.
ZnO semiconductor surface resistivity is also subject to operational environment including oxygen concentration, moisture and an organic molecule.
Accordingly, the applicant proposed an ultraviolet light detecting element described in Patent Literature 1.
The ultraviolet light detecting element mentioned above uses an embedded type electrode in order to suppress an influence of electrically unstable film surface as much as possible and to control a variation in electrical characteristics for each element.